Apart from barley malt, unmalted cereals such as wheat are commonly used in beer production (Pierce, J. S., Proceedings of the European Brewery Convention Congress, Madrid, 1987, 445). Unmalted wheat (40-50%) is e.g. used for the production of Belgian white (wheat) beers.
Although barley and wheat endosperm cell walls contain 20 and 70% (w/w) arabinoxylan respectively (Ballance, G. M., & Manners, D. J., Carbohydrate Research, 1978, 61, 107; Fincher, G. B., & Stone, B. A. In: Advances in Cereal Science and Technology, Vol. VIII. Y. Pomeranz, (Ed), Am. Assoc. Cereal Chem., St. Paul (MN), 1986, 207), their total arabinoxylan content is comparable, i.e. 2.8 to 7.1% (w/w) for barley and 3.6 to 7.1% (w/w) for wheat (Henry, J., Journal of the Science of Food and Agriculture, 1985, 36, 1243; Hashimoto, S., Shogren, M. D. & Pomeranz, Y., Cereal Chemistry, 1987, 64, 30).
The grains also contain comparable levels of water-extractable arabinoxylan, i.e. 0.24 to 0.80% (w/w) for barley and 0.25 to 1.18% for wheat (Henry, J., Journal of the Science of Food and Agriculture, 1985, 36, 1243; Hashimoto, S., Shogren, M. D. & Pomeranz, Y., Cereal Chemistry, 1987, 64, 30; {dot over (A)}man, P., & Hesselman, K., Swedish Journal of Agricultural Research, 1984, 14, 135; Girhammer, U., & Nair, B. M., Food Hydrocolloids, 1992, 6, 285). Furthermore, barley and wheat endosperm cell walls contain 70 and 20% β-glucan respectively (Ballance, G. M., & Manners, D. J., Carbohydrate Research, 1978, 61, 107; Fincher, G. B., & Stone, B. A. In: Advances in Cereal Sciences and Technology, Vol. VIII. Y. Pomeranz, (Ed), Am. Assoc. Cereal Chem., St. Paul (MN), 1986, 207).
Barley grains contain 1.7 to 4.1% (w/w) water-extractable and 3.6 to 6.4% (w/w) total β-glucan (Anderson, M. A., Cook, J. A., & Stone, B. A., Journal of the Institute of Brewing, 1978, 84, 233-239; Henry, J., Journal of the Science of Food and Agriculture, 1985, 36, 1243). Wheat grains contain 0.1 to 0.8% (w/w) water-extractable and 0.6 to 1.4% (w/w) total β-glucan (Anderson, M. A., Cook, J. A., & Stone, B. A., Journal of the Institute of Brewing, 1978, 84, 233-239; Henry, J., Journal of the Science of Food and Agriculture, 1985, 36, 1243). As in wheat only low levels of arabinoxylan (Cleemput, G., Bleukx, W., van Oort, M., Hessing, M. & Delcour, J. A., Journal of Cereal Science, 1995, 22, 139) and β-glucan degrading enzyme activities can be measured, the barley malt must be mostly responsible for wheat and malt arabinoxylan and β-glucan hydrolysis during brewing.
Efficient hydrolysis of arabinoxylans and β-glucan is important because such compounds can be involved in production problems such as wort viscosity (Ducroo, P. & Frelon, P. G., Proceedings of the European Brewery Convention Congress, Zurich, 1989, 445; Viëtor, R. J. & Voragen, A. G. J., Journal of the Institute of Brewing, 1993, 99, 243) and filterability and haze formation (Coote, N. & Kirsop, B. H. 1976., Journal of the Institute of Brewing, 1976, 82, 34; Izawa, M., Kano, Y. & Kanimura, M. 1991. Proceedings Aviemore Conference on Malting, Brewing and Distilling, 1990, 427).
In other areas efficient hydrolysis of xylans and/or arabinoxylans is highly desirable as well. Examples include rye and wheat breadmaking processes, paper and pulp technologies. It follows that a lot of research efforts have been devoted to the (potential) applications of xylan and/or arabinoxylan hydrolysis enzymes due to their applications as described above.